Schalke chief Christian Heidel won't shut the door on signing outright Abdul Baba Rahman.
The Ghana fullback joined S04 last month on a straight loan, without a permanent option.
However, Heidel insists the player could yet be persuaded to stay.
He explained: "His situation is a bit different. Chelsea is a bit more restrictive.
"In the end it depends then the player on whether he wants to stay with us. "